1. Field of the Invention
The present invention relates to b-stageable die attach adhesives, methods of preparing such adhesives, methods of applying such adhesives to the die and other substrate surfaces, and assemblies prepared therewith for connecting microelectronic circuitry.
2. Brief Description of Related Technology
Bismaleimides occupy a prominent position in the spectrum of thermosetting resins, and a number of bismaleimides are commercially available. Bismaleimides have been used for the production of moldings and adhesive joints, heat-resistant composite materials, and high temperature coatings. More recently, Henkel Loctite Corporation has commercialized a number of products based in part on certain bismaleimides for the attachment of semiconductor chips to circuit boards, which have been well received commercially from within the microelectronic industry. These products are covered in one or more of U.S. Pat. No. 5,789,757 (Husson), U.S. Pat. No. 6,034,194 (Dershem), U.S. Pat. No. 6,034,195 (Dershem) and U.S. Pat. No. 6,187,886 (Husson).
It would be desirable to provide the die attach material in a b-stageable form, such as a wafer-applied or substrate-applied version thereof. Such a version would eliminate many of the storage, dispensing, handling and processing issues that exist when dispensing in a flowable form reactive adhesives, including die attach adhesives.
B-stageable of pre-applied adhesives themselves are not a new commercial entity. For instance, Henkel Loctite has a substantial business in pre-applied threadlocker adhesives, which involve (meth)acrylate chemistry, for use in connection with nut and bolt assemblies, curable by either a photocure mechanism, a heat cure mechanism, or combinations thereof, with an optional secondary anaerobic cure mechanism. See also U.S. Pat. Nos. 2,928,446, 4,325,985, 4,632,944 and 5,300,608.
In addition, pre-applied underfill encapsulants have also been designed and developed by Henkel Loctite (see International Patent Application No. PCT/US00/07494).
However, to date there has not been a b-stageable heat curable composition based on the combination of a liquid and a solid curable component, or articles of manufacture placed in commerce, such as a semiconductor chip or a semiconductor wafer, with such a b-stageable die attach adhesive preapplied thereon for application without the intermediate process steps for the microelectronics packaging or assembling end user attendant with a flowable die attach adhesive.